The present invention relates to an object detecting apparatus for detecting the distance to an object and the presence or absence of the object.
It has been known to detect the distance to an object by measuring a time interval from an instant that light, acoustic wave, microwave, or the like is projected onto an object until the portion of the wave reflected by the object is returned to the wave projecting point. In an application of this method, it is possible to detect the presence or absence of an object by comparing the measured time with a reference time. Recently, object detecting devices based on such methods have found a wide use in a variety of fields. A television set incorporating the object detecting apparatus will be described. It is generally said that an optimum distance between the TV set and a human viewer for watching the television is five to seven times the longitudinal length of the TV set to protect the eyes of the viewer. In viewing the television, the viewer tends to unconsciously excessively approach the television screen. To cope with this problem, it is recommendable to install in a TV set an object detecting apparatus which is designed so as to operate in the following way. When a viewer approaches the TV screen closer than a given distance, the object detecting apparatus issues an alarm, while continuously checking the distance between the viewer and the TV set. The alarm may comprise a voice saying "You are too close to the TV set! Move away a little" produced by a voice synthesizer. Coversely, when the viewer moves away from the TV set beyond another given distance, the object detecting apparatus turns off the power switch of the TV set, judging that the viewer has ceased to watch the TV. Further, when the viewer approaches the TV set within that distance, the apparatus automatically turns on the power switch. This approach is very useful in that it protects the eyes of viewer and saves the electric power.
Generally, in a room with the TV set, there are many objects such as a chair, desk, bookshelf and the like, in addition to a human viewer. When using the object detecting apparatus, it is difficult to strictly discriminate the wave reflected by the viewer from waves reflected by the other objects. This discrimination is roughly possible because the amplitude of the reflecting wave depends on a size of the object. However, when the size of the object is comparable to that of the viewer, the discrimination is almost impossible.